Change getSystemUiStateString to not contain excess pipe characters

This changes the string from
`|overview_disabled||||||keygrd_visible||||||||||allow_gesture||||device_dozing||||||`
to
`overview_disabled|keygrd_visible|allow_gesture|device_dozing`
for better readability

This change also formats the SYSUI_STATE_SCREEN_TRANSITION and SYSUI_STATE_SCREEN_ON
flags as individual flags instead of a enum. The rationale is that
otherwise its impossible to use getSystemUiStateString to produce a
string for masked, unrelated flags, as it would always append
`screen_off`

Bug: b/261418621
Test: Checked log output manually
Change-Id: Ia0d3320d683d4e61faa4f5f4910d1dcc69be79e6